1. Field of the Invention
The invention relates to a sliding member used for an oil seal and the like.
2. Description of Related Art
An oil seal is assembled on a rotating shaft for an engine of an automobile in order to prevent, for example, leakage of oil through an end of the rotating shaft, and conversely, entry of external dust. The oil seal needs to be highly resistant to heat and oil. Thus, fluorine rubber is often used as a formation material for a sliding member used for the oil seal. For the oil seal, there has also been a request for a substantial reduction in sliding torque in order to meet recent demands for energy saving and an extended life of the oil seal.
Thus, effort has been made to cover a sliding surface of a seal lip on which the rotating shaft slides with a coating that enables friction to be reduced and that is highly resistant to wear. Japanese Patent Application Publication No. 2003-165856 (JP 2003-165856 A) discloses that a sealing material (O ring) for a manufacturing apparatus for semiconductor devices and the like is formed of fluorine rubber and that a surface of the sealing material is covered with a coating that is formed of a silicone resin, a fluorine resin, or a polyimide resin and in which fluorine resin powder is dispersed.
This coating contains the fluorine resin powder that functions as a solid lubricant and thus enables friction to be reduced, and is also highly resistant to wear. Thus, such a coating is expected to be used to cover a sliding member such as an oil seal.
However, when the conventional coating is used for the sliding member such as an oil seal, the coating may fail to withstand sliding of the rotating shaft or the like, which rotates at high speed, and crack in a short period of time or may be likely to be peel off in a short period of time due to insufficient adhesion to the oil seal, which serves as a base. When the coating cracks, sealing performance may be significantly degraded in a short period of time based on a change in contact form resulting from the destruction of the base material. Furthermore, when peel-off of the coating starts at the position of the crack, the capability of reducing friction is lost, and the sliding torque may increase significantly in a short period of time.